A. Field of the Invention
This invention relates generally to heat furnaces and specifically to a device for preventing the escape of heated air from the heat exchanger when the burner is not operating but allowing the flow of flue gases through the heat exchangers during burner operation.
B. Description of the Prior Art
The invention is applicable to standard furnaces, including atmospherically vented gas fired furnaces. Such a furnace typically includes one or more burners, a heat exchanger, a blower, and a venting system. The blower circulates air through the furnace. When the burner is operating, combustion products flow upward into and through the heat exchanger, transferring heat to the heat exchanger. The heat exchanger in turn transfers heat to conditioned air being circulated through the furnace. The combustion products in the heat exchanger exit the heat exchanger through the heat exchanger outlets and usually are mixed in the drafthood with ambient air admitted through the permanently open drafthood relief opening. The combustion products/air mixture then exits the furnace through an opening in the top of the drafthood and enters a vent connector which is part of the venting system. The venting system then exhausts the combustion products into the atmosphere.
The above described furnaces have inherent inefficiencies when the burner is not operating. At the completion of the burner cycle, the heat exchanger is still warm. However, air continues to flow through the flue gas passages of the heat exchanger and absorbs heat, thereby cooling the heat exchanger. The warmed air then flows into the venting system where it is exhausted outdoors. As a result, heat is wasted, thereby decreasing the efficiency of the heat furnace.
One attempted solution to this problem consisted of a vent damper installed in the vent connector. Such a vent damper closed the vent connector while the burner was not operating so that the stored heat was transferred to air exited through the drafthood relief opening instead of through the venting system. In such a system, the transferred heat would exit directly from the furnace and would be wasted if the furnace was installed in an unconditioned space. Thus, the heat would still be wasted unless the furnace itself was installed in a conditioned space. In addition, the installation of the vent damper also required extra time and expense, as well as other problems associated with installation, such as possible improper wiring or the selection of the wrong device. As a result, the vent damper approach provided a partial solution, at best.